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Characterization of human presenilin 1 using N-terminal specific monoclonal antibodies: Evidence that Alzheimer
M Mercken1, H Takahashi, T Honda
1Mitsubishi Kasei Institute of Life Sciences, Tokyo, Japan.
Insights
Mutations in the presenilin 1 (PS1) gene cause early-onset familial Alzheimer disease. Impaired processing of the PS1 protein, not the mutation itself, may lead to disease development.
Area of Science:
- Neuroscience
- Genetics
- Molecular Biology
Background:
- Early-onset familial Alzheimer disease (FAD) is often linked to mutations in the presenilin 1 (PS1) gene.
- The PS1 protein is integral to cellular membranes and plays a role in Alzheimer disease pathogenesis.
Purpose of the Study:
- To investigate the processing of the presenilin 1 (PS1) protein in relation to Alzheimer disease mutations.
- To characterize the molecular products of PS1 and their relevance in familial Alzheimer disease.
Main Methods:
- Production of monoclonal antibodies targeting the N-terminal hydrophilic tail of PS1.
- Detection of PS1 protein products (47 kDa and 28 kDa) in human brain and cell line membrane extracts.
- Analysis of PS1 processing in PC12 cells transfected with wild-type and mutant PS1 constructs.
Main Results:
- Monoclonal antibodies successfully detected full-size PS1 (47 kDa) and a prominent 28 kDa product.
- PC12 cells expressing wild-type PS1 generated the 28 kDa product, while cells with Alzheimer mutations did not.
- This suggests impaired proteolytic processing of PS1 in the presence of specific mutations.
Conclusions:
- Missense mutations in PS1 associated with familial Alzheimer disease may impair the protein's proteolytic processing.
- This impaired processing could be a key mechanism underlying the pathogenesis of early-onset familial Alzheimer disease.
Abstract:
The majority of cases of early-onset familial Alzheimer disease are caused by mutations in the recently identified presenilin 1 (PS1) gene, located on chromosome 14. PS1, a 467 amino acid protein, is predicted to be an integral membrane protein containing seven putative transmembrane domains and a large hydrophilic loop between the sixth and seventh membrane-spanning domain. We produced 7 monoclonal antibodies that react with 3 non-overlapping epitopes on the N-terminal hydrophilic tail of PS1. The monoclonal antibodies can detect the full-size PS1 at Mr 47000 and a more abundant Mr 28000 product in membrane extracts from human brain and human cell lines. PC12 cells transiently transfected with PS1 constructs containing two different Alzheimer mutations fail to generate the 28 kDa degradation product in contrast to PC12 cells transfected with wild-type PS1. Our results indicate that missense mutations in this form of familial Alzheimer disease may act via a mechanism of impaired proteolytic processing of PS1.